1. Field of the Invention
The invention relates to a secondary battery and the fabrication method thereof, and more particularly, to a secondary battery and the fabrication method thereof which improves the efficiency of feeding of an insulating member to the inside of a container, suppresses the occurrence of the bend of the insulating member, and prevents the insulating member inserted into the inside of the container from escaping from the container.
2. Discussion of Related Art
Generally, secondary batteries are rechargeable and dischargeable batteries which are different from the non-rechargeable primary batteries, and are widely used in high technology electronic devices, such as cellular phone, notebook computer, camcorder, etc. In particular, the use of a lithium secondary battery has rapidly increased because it has an operating voltage of 3.6V which is 3 times as high as that of nickel-cadmium battery or a nickel-hydrogen battery used as a power supply for an electronic device, and it has a high energy density per weight.
The lithium secondary battery generally uses a lithium-based oxide as a positive electrode active material and a carbon material as a negative electrode active material. Furthermore, the lithium secondary battery has been made in various shapes of which typical configurations are cylindrical, polygonal and pouched shapes.
The polygonal secondary battery includes an electrode assembly, a can receiving the electrode assembly and a cap coupled with the can.
The electrode assembly includes the positive electrode, the negative electrode and a separator interposed between the positive electrode and the negative electrode, and the electrode assembly is jelly-roll wound, and positive electrode tab and negative electrode tab protrude from the positive electrode and the negative electrode, respectively.
In the polygonal secondary battery, the can has a rectangular parallelepiped shape made of metal, and is formed by a processing method such as a deep drawing method.
The cap includes a cap plate coupled with the upper part of the can, an electrode terminal which is mounted through a hole of a terminal and is provided on its outer surface with a gasket for insulating from the cap plate, an insulating plate mounted on the underside of the cap plate, and a terminal plate which is mounted on the underside of the insulating plate and is electrically connected with the electrode terminal.
One electrode of the electrode assembly is electrically connected to the electrode terminal via the electrode tab and the terminal plate, and the other electrode is electrically connected to the cap plate or the can via the electrode tab coupled thereto.
In addition, an insulating member can also be provided on the lower part of the terminal plate. The insulating member serves for insulating between the electrode assembly and the cap.
However, there are problems in the conventional insulating member as follows:
First, the injection of the raw material for the conventional insulating member takes place, upon considering the plate as a reference, in the opposite side to the side on which sidewalls are to be formed. Namely, if the sidewalls of the insulating member are extended upwardly in the plate, then the injection of the raw material takes place toward the plate in the lower side of the plate. Thus, “a spot of injecting the raw material” leaves which is defined as a spot formed after the raw material is injected onto the lower surface of the plate. In this spot, a burr which refers to a raised potion formed on the lower surface of the plate after the raw material is injected onto the lower surface of the plate is formed. Accordingly, when an injection-molded insulating member is inserted into the inside of the can by a feeding machine and positioned over the electrode assembly, the insulating member has to be positioned in the target position so that the feeding machine can grasp well the insulating member, however, the lower surface of the plate cannot be maintained flat by the burr formed thereon, and thus the insulating member cannot be positioned in place and can be moved. That is, a problem is arisen that the grasping of the insulating member by the feeding machine becomes difficult due to the scattering of the position of the insulating member, and thus the feeding efficiency is lowered. In order to solve this problem, a burr protruded from the lower surface of the plate has to be removed, which necessitates a separate process, time and cost.
Second, a remaining heat still remains in the insulating member separated from the mold after the solidification, and thus a contractile stress is produced therein. That is, since the injection of the raw material for the conventional insulating member takes place, upon considering the plate as a reference, in the opposite side to the side on which sidewalls are to be formed, a problem is arisen that the insulating member is bent in the direction opposite to that of injecting the raw material.
Third, upon inserting the insulating member into the inside of the can, it is necessary to take measures in order that the insulating member cannot be escaped out of the can during the fabrication process of the secondary battery. For this purpose, a method is conceivable that an inversely stepped can having the periphery of the upper inner wall which is longer than the periphery of the lower inner wall is used so that the sidewalls of the inserted insulating member can be caught on the inversely stepped part of the can and cannot be escaped out of the can. However, the plate makes an acute angle with the outer surface of the sidewalls. In case that the plate makes a right angle with the outer surface of the sidewalls, it is difficult to separate downwardly the lower case with respect to the upper case without damage of the insulating member, and thus the plate should makes an acute angle with the outer surface of the sidewalls. Accordingly, a case that the sidewalls of the insulating member inserted into the inside of the can cannot be caught on the inversely stepped part of the can is occurred, a problem that the insulating member escapes out of the can is arisen.